The present invention relates to a water treating apparatus and, more particularly, to an apparatus for feeding the influent raw water into a center post clarifier.
It is well known in the water treating and clarification art that suspended solid particles act as "seed" or nuclei to which newly formed precipitates adhere, creating a smaller number of larger, more dense and easily settled particles. Previously formed precipitates act as the "seed" to speed the reactions between the incoming raw water and treatment chemicals. A particularly successful apparatus for clarifying water is disclosed in U.S. Pat. No. 3,473,665, assigned to the same assignee as the present invention. This apparatus hydraulically recirculates settled precipitates or sludge upwardly into an uptake zone for mixing with the incoming raw water and chemical treating agents. Flow control means are provided to compensate for varying liquid throughput rates so as to ensure the presence of an optimum supply of recirculated precipitates to accomplish coagulation and clarification.
Many of the older water and waste treatment plants presently include conventional center post clarifiers which have no provisions for recirculation of sludge and consequently do not operate as efficiently as the apparatus mentioned immediately hereinabove. Previous attempts to upgrade these clarifiers have included the addition of tube settling devices or the reconstruction of the center post, which is the major structural member of the clarifier. These upgrading techniques are not very practical because they involve the installation of additional and/or auxiliary equipment which is very expensive.
Accordingly, it is a primary object of the present invention to provide a center post clarifier which hydraulically recirculates solid precipitates or sludge upwardly into contact with the incoming raw water and added chemical agents.
Another object is to provide such a clarifier which includes means to selectively control the sludge recirculation rate.
A further object of the present invention is to provide a center post clarifier design which hydraulically recirculates solid precipitates or sludge and may be adapted to existing center post clarifiers by the installation of a few inexpensive non-moving parts.
These and other objects are realized in accordance with the present invention by providing a center post clarifier having an uptake zone defined around the center support post forming an eductor tube having an upper and lower end respectively in communication with an upper and lower portion of the mixing and recirculation chamber. A first set of openings is provided intermediate the center post for directing the flow of raw water upwardly into an intermediate portion of the uptake zone. A second set of openings positioned above the first set of openings is provided for directing the remaining flow of raw water from the center post into an upper portion of the uptake zone. The relative flow rates of raw water through the first and second openings being such as to cause sludge which has accumulated adjacent the lower end of the uptake zone to be lifted thereinto and recirculated with the raw water. Unique means are provided to selectively control the flow rates of raw water through the first and second openings to adjust the sludge recirculation rate.